Apparatus for displaying waveforms of time-varying signals emloying a television type display

ABSTRACT

Television display system for displaying the waveform of a timevarying input signal. The displayed waveform moves across the display screen. The scanlines of the raster scan-line pattern are traced on the display screen in a direction orthogonal to the direction of movement of the waveform. The waveform image is constructed on the display screen by writing along each scanline between two data points which are obtained from adjacent samples of the input signal.

United States Patent 191' Graves et al. Oct. 9, 1973 [54] APPARATUS FORDISPLAYING 3,590,3ll 6/1971 Stone 340/324 A WAVEFORMS TIME VARYING3,474,438 /1969 Lauher 340/324 A 3,343,030 9/1967 Dragon et a]. 340/324A SIGNALS EMLOYING A TELEVISIONTYPE 3/1972 Metz et al. 340 324 ADDISPLAY [73] Assignee GTE Sylvania Incorporated, 7 I

Stamford, Conn.

[22] Filed: Mar. 1', 1972 21 Appl. No.: 230,708

U.S. Cl. 340/324 A, 235/198 Primary Examiner-John W. Caldwell AssistantExaminer Marshall M. Curtis Att0rney-Norman J. OMalley et a1.

[ ABSTRACT Television display system for displaying the waveform of atime-varying input signal. The displayed waveform moves across thedisplay screen. The scanlines of [521 the raster scan-line pattern aretraced on the display [51] r 3/14 screen in a direction orthogonal tothe direction of [58] Field of Search 340/324 A, 324 AD; movement f thewaveform The v f image is 235/197; constructed on the display screen bywriting along each scanline between two-data points which are ob- [561References C'ted tained from adjacent samples of the input signal.UNITED STATES PATENTS 3,406,387 10/1968 Werme 340/324 AD 7 Claims, 7Drawing Figures 719 46 41 ANALOG WAVEFORM ERASE WAVEFORM INPUTS 1| copeTEMPORARY PREVIOUS No GENERATOR REG'STERS REGISTER T D. 2 I -17 '25 vCOMPARATOR 1 RANDOM :fi A/D 1 ffi ACCESS gg? WAVEFORM MUX *WRTERREGISTER MUX DIGITAL PRESENT may STORAGE REGISTER v I MEMORY H43 LARGESMALL NUMBER NUMBER N04 ADDRESS a/ COUNTER COUNTER CODE a/N INPUT d/NMUX REGISTER T l l REGISTER CLOCK CLOCK l FF 61 36 UN 5 CHARACTER MUXGENERATOR 2o 1 .2 MTA'SAEERR :9 1 71 53 TIMING so .REGISTER MARK INPUT 1OUTPUT UNTER COUNTER GENERATOR NO.1 No.1

a/N 55 v 33 crocxf ,.72 57 1 REFRESH 29 31 INPUT OUTPUT ADDRESS ICOUNTER COUNTER COUNTER RATE DlVlDER NO. 2 NO. 2 ge rgii 2: ,44 cLocKfas MUXY CLOCK s E INPUT OUTPUT f/x 2 COUNTER COUNTER 3o Nola Nola 35ctocKi /74 INPUT 7 OUTPUT OSCILLATOR COUNTER COUNTER CLOCKl PATENTEUuc-I9 1915 SHEET REF 4 QUADRANT 4 EACH I QUADRANT 896 WAVEFORM 12a a/N CODESHEIGHT CODES (4 ROW S, (89 6 VERTICAL SCAN LINES) 32 CHARACTERS/ROW) mtmw mrEm w QUADRANT 1 QUADRANT 2 QUADRANT 3 QUADRANT 4 TOTAL MEMORY 5PATENTEUUCT 9 1911 1 3,765,009

SHEET & [1F 4 INPUT 'couNTER OUTPUT VALUE 1 COUNTER AT START VALUE OFFIELD r 215 PRESENT QUADRANT 1 215 DATA 214 PREvIouS DATA 701 PRESENTuADRANT 2 7 1 DATA F'RST Q 0 PREvIous SCAN LINE 700 DATA I PRESENT ODD AA T 2 2 DATA 0 DR N 3 FIEL QU A 1 PREv1ous DATA I PRESENT QuADRANT4 105105 DATA 104 PREvIous k DATA RETRAcE 213 PRESENT QuADRANT 1 21s DATA I212 PREvIous DATA - 699 PRESENT E ND QUADRANT 2 701 DATA ScAN LINE 698PREVIOUS- IN DATA 000 I I PRESENT HELD QUADRANT 3 2 0 DATA 895 PREVIOUSDATA - PRESENT QuADRANT 4 105 103 DATA 102 PREVIOUS DATA RETRAcE 211PRESENT QUADRANT 1 215 DATA 210 PREvIous DATA THIRD scAN LINE IN ODDFIELD I Fig.

. 1 APPARATUS FOR DISPLAYING WAVEFORMS OF TIME-VARYING SIGNALS EMLOYINGA TELEVISION TYPE DISPLAY BACKGROUND OF THE INVENTION beam during ahorizontal sweep in accordance with the amplitude of the signal.

Apparatus of this type is widely used and it works particularly well forproviding visual images of repetitive, high-frequency signals. However,the oscilloscope is not particularly well suited to provideasatisfactory display of non-repetitive signals when only. a single.trace of each signal can be placed on the surface of th tube.

One class of signals of this type which are of particu lar significanceare physiological signals such I as electro-eardiographic and othermeasurements for monitoring the life signs of a human being, inparticular, a patient in an intensive care unit of a hospital. Thewaveforms developed from the information sensed are relatively slow andoften are non-repetitive. Strip-chart recorders which continuously plotthe amplitude of the waveforms while calibrated paper is moved along thedirection of the time axis are widely employed for producing visualdisplays of these signals. These devices are particularly usefulwhenever it is desired to provide v a visual image which is to beretained. However, stripchart recorders usually produce large quantitiesof unwanted paper, and by virtue of their mechanical nature have poorfrequency response and are subject to various forms of mechanicaldifficulties. 7

More recently therehas been developed televisionlike display apparatusin which a waveform appears to move across the face of acathode ray tubesimulating the viewing of a strip-chart recorder display through awindow. In apparatus of this type the data is written into a memory at aslow real time rate and is read out quickly and repetitively insynchronism with the raster scanline pattern for display on the cathoderay tube. The data in the memory is replaced as new data is obtained-andthe stored data is employed to continually update the display on thecathode ray tube during repeated sweeps of the raster scanline pattern.

Apparatus of this type typically employs a digital delay line as amedium for storing the data. The length of the delay line is selected sothat the data recirculates at such a rate that each slow incoming samplereplaces the oldest piece of data in the memory, thus gradually updatingthe memory so that it contains a history of the most recent information.The data recirculates at such a rate that as the data is read out fordisplay, the most recent data is displayed at one edge of the screen andthe oldeststored data at the opposite edge. Constant replacing of theold data with new data causes the disviewing of a strip-chart recorderdisplay through a window. i

Typically, the waveform is constructedon the screen by writing a seriesof dot images outlining the waveform during each sweep of the rasterscanline pattern. Each dot image is written at a data point, thevertical position of which is determined by the data content of a pieceof data read out of the memory and the horizontal position of which isdetermined by the time during the sweep at which it is read out of thememory.

Waveforms constructed in this manner may have discontinuities or gaps inthe displayed image due to rapid changes in amplitude occurring duringhigh frequency signals. In addition, the aesthetic and readabilityqualities of waveforms constructed of a series of equalsize dots'are notespecially high.

SUMMARYOF THE INVENTION Apparatus in accordance with the presentinvention improved aesthetic and readability qualities. The apparatusincludes means for receiving a time-varying signal and sampling meansfor periodically sampling increments of the signal. The apparatus alsoincludes means for converting the sampled increments of the signal todigital representations thereof and memory means for storing apredetermined number of the digitial representations. The most recentdigital representation is loaded into the memory means in place of theoldest digital representation stored therein by an input control means.

' The apparatus includes'display means of the type producing images on adisplay surfaceby selectively writing on the display surface whilerepeatedly sweeping a raster scanline pattern over the display surface.Output means coupled to the memory means and to the display means causetwo digital representations which areread out of the memory means foreach scanline of the raster scanline pattern to produce an :image on thedisplay surface during tracing of the scanline from a pointrep'resentative of the value of one digital representation to a pointrepresentative of the value of the other digital representation. outputcontrol means read two digital representations out of the memory meansfor each scanline of the raster scanline pattern and cause the digitalrepresentations to be readout in synchronism with the sweeping of theraster scanline pattern so that images of the most recent digitalrepresentations appear at one edge of the display and images of theoldest digital representations appear at the opposite edge-of thedisplay.

BRIEF DESCRIPTION OF THE DRAWINGS cordance with the present invention;

FIG. 2 is a representation of the display surface of a display deviceemployed in the system of FIG. 1 illustrating the display oftime-varying waveforms and fixed alphanumeric characters;

FIG. 3 is a chart or map of a random access digital storage memoryemployed in the system of FIG. 1 indicating the storage locations ofwaveform and alphanumeric character data;

FIG. 4 is a chart diagramming an input and output cycle of the memory;

FIG. 5 is a diagram illustrating the manner in which images of waveformdata are combined to construct a waveform shape on the display surfaceof the display device of the apparatus;

FIG. 6 is a chart useful in explaining the operation of the system ofFIG. 1 in reading out waveform data from the memory for display on thedisplay device; and

FIG. 7 is a block diagram of a counter employed in addressing the memoryto control the reading out of alphanumeric character data from thememory for display on the display device.

DETAILED DESCRIPTION OF THE INVENTION General Description A displaysystem in accordance with the present invention which is particularlyadapted for use in monitoring physiological signals is illustrated inblock diagram form in FIG. 1. FIG. 2 illustrates the display surface ofa television-type cathode ray tube display 10 employed with the systemof FIG. 1. As shown in FIG. 2, a moving waveform, for example, anelectrocardiographic waveform, is displayed on the face of the cathoderay tube. In the embodiment shown only the upper quadrant of the displaysurface is used for displaying the waveform. New data is entered at theright of the waveform and precesses across the display until itdisappears at the left. In addition to the moving waveform, alphanumericcharacters which remain fixed in position may also be displayed on thedisplay surface. Similarly, independent waveforms and alphanumericcharacters appear in the other three quadrants onthe display surface,although not illustrated in FIG. 2.

Throughout the present description actual values of a specificembodiment of the invention are given. It is believed that the use of asingle set of specific related values simplifies the explanation of theinvention. However, it should be borne in mind that many variations andmodifications are obviously possible within the scope of the invention.

In the apparatus as illustrated in FIG. 1 four different analog waveformsignals (one for display in each of the four quadrants on the displaysurface of the display device 10) may be received on four differentinput channels applied to the inputs of four respective input amplifiersll, 12, 13, and 14. The amplifiers are employed to adjust the signalamplitudes and offset biases and ,to filter out high frequency noise.The analog waveform signals from the amplifiers are applied to amultiplexer where they are sampled sequentially at a rate ofapproximately 240 samples per second for each waveform under the controlof signals from an oscillator and divider and gates arrangement 31. Thetimemultiplexed sampled increments are applied to an analog-to-digitalconverter 16, and the digital data is stored in a register 17.

The stored digital datain the register 17 is loaded into a random accessdigital storage memory 25 by a multiplexer 18. The appropriate addressfor each piece of digital data is controlled separately for each channelby respective input counters 32, 33, 34, and 35. The

input counters receive input pulses at individually selected rates. Thepulses are generated by the oscillator 30, and the rates at which theyare applied to the input counters is determined by settings ofmanuallyoperated rate control switches 29 which control the divider andgates arrangement 31. The states of the input counters 32, 33, 34, and35 designate the storage locations in the memory 25 in which the mostrecent digital data stored in the register 17 from the correspondingwaveform input channels is to be stored. This address information isapplied to the memory 25 through multiplexers 36 and 28. Thus, thestorage addresses of incoming data and the rate at which it is acceptedfor storing is individually controlled for each waveform.

Alphanumeric information is applied to the system at an alphanumericinput and loaded into an alphanumeric register 27. The alphanumericinformation received includes digital code words each designating analphanumeric character and an address code designating the storagelocation in the memory 25, which code also designates the position ofthe character on the display. The alphanumeric data passes through themultiplexer l8 and the address data passes through multiplexer 28causing the alphanumeric data to be stored in the proper location in thememory 25.

Waveform data is read out of the random access digital storage memory 25under control of the input counters 32, 33, 34, and 35 and outputcounters 71, 72, 73, and 74. The counts stored in the input counters 32,33, 34, and 35 are loaded into the output counters 71, 72, 73, and 74.The output counters count downward on clock pulses and the countinformation is applied through a multiplexer57 and the multiplexer 28 toaddress the storage locations of the random access digital storagememory 25 to be read out. As will be explained in more detailhereinbelow, two adjacent pieces of data on each waveform are read outof the memory 25 and loaded into a waveform previous register 1 and awaveform present register 42. The data in these registers is compared ina comparator 44, and then appropriately loaded into a small numbercounter 51 and a large number counter 52. These counts control theoperation ofa flip-flop 54, the output of which passes into a summingnetwork 55 to become part of the composite video signal applied to thedisplay device 10.

Readout of the alphanumeric data from the memory 25 is controlled byalphanumeric refresh address counter 60. The address information isapplied to the memory 25 through the multiplexer 28. The alphanumericdata readout of the memory 25 passes to an alphanumeric code register 43and from there to an alphanumeric character generator 45 which alsoreceives information from the alphanumeric refresh address counter 60.The output of the alphanumeric character generator 45 is applied to aregister 53 from which it passes through the summing network 55 tobecome part of the composite video signal applied to the display device10.

Also shown in FIG. 1 is a matter timer 61 which supplies timing andcontrol signals to the various porto the other element of the apparatusso as to properly coordinate operations throughout the system.

In the specific embodiment of the apparatus described herein thewaveforms from four channels of physiological information are displayedon the display device 10. As illustrated in FIG. 2, each waveform isdisplayed within a different one of the four vertically arrangedquadrants on the display surface of the display device 10. each waveformappears to move from right to left across the display with the newestdata appearing at the right and the oldest data appearing at the left.Each waveform may be made to precess, for example, at rates whichpresent from 3.7 to 14.8 seconds of data for display at one time. Eachquadrant of the display surface may also display up to four rows ofalphanumeric characters. Up to 32 characters may be displayed in eachrow. The characters displayed may be selected from he full ASCIIrepertoire of '64 characters.

The display device employs a'high resolution raster of 1023 scanlineswith odd and even lines interlaced in alternate fields. Each individualscanline sweepsvertically from the top to the bottom of the display andthe raster of scanlines is swept across thedisplay from the right edgeto the left edge. The rasterscanline pattern is swept at a rate of 60fields per second, or 30 complete frames per second. The period of eachscanline is 32.5 microseconds. Each scanline has an active trace periodof 26 microseconds (6.5 microseconds per quadrant) and a retrace time of6.5 microseconds. Of the total of 1023 scanlines swept through in acomplete frame 896 scanlines are employed for the display.

As illustrated in FIG. 2 each quadrant of the display is divided intofive sectors 62, 63, 64, 65, and 66. The first, second, fourth, andfifth sectors 62, 63, 65, and 66 contain the four rows of alphanumericcharacters. (Only three rows are utilized for displaying characters inthe illustration of FIG. 2) All five sectors of the quadrant areutilized to display the waveform. The maximum vertical excursion of eachwaveform encompasses 128 evenly-spaced points along the vertical heightof the quadrant. The waveform illustrated in FIG. 2 has maximum andminimum points which are well within the possible limits. The digitaldata representing each sample of the waveform designates one of the 128points corresponding to the amplitude of the sample. Each alphanumericcharacter including the spacing to the next character, encompasses awidth of 14 raster scanlines in both the odd and even fields.

Memory FIG. 3 is a map of the random access digital storage memory 25.The memory may be any of the various well-known types of random accessmemories, such as an MOS type. In the specific embodiment shown hereinthe memory is a 4096-word memory with 7-bit words. The memory isorganized into four l024-word groups, each corresponding to a differentquadrant of the display. Each quadrant includes 896 7-bit stagescontaining 896 digital representations of samples of the waveform of thecorresponding channels, one stage for each active vertical scanline ofthe display. The 7-bit stages permit encoding of data to designate oneof the 128 vertically arranged points in the appropriate quadrant of thedisplay.

In addition, each quadrant includes 128 6bit stages (the 7th bit in eachstage is not used) for containing digital code words representingalphanumeric characters. Each stage is associated with a specific one ofthe 32 character positions of one of the four rows of alphanumericcharacters to be displayed in the quadrant of the display. The 6-bitwords permit encoding to designate any one of the 64 possiblealphanumeric characters available for display.

The stages of the memory 25 for containing the waveform data areaddressed in sequence for writing into the memory so that the oldeststored data is replaced by the most recent data received. The stages areaddressed for reading out of the memory so that the data is displayed onthe display surface with the most recent data at the right and theoldest data at the left. Alphanumeric data applied to the memory isassociated with address data for storing the data in predeterminedstages, which when addressed at readout designate specific positions onthe display.

Data Input Information received at each of the four waveform inputchannels is sampled by the multiplexer 15, the sampled incrementsconverted to digital format by the analog-to-digital converter 16, andthe digital data stored in the register 17. Data in the register isloaded into the proper stage of the memory 25 to replace the oldeststored piece of data related to the same waveform. For each channel thewaveform is sampled and the data in the register 17 is updated at therate of approximately 240 times per second. The rate at which datatransferred from the register 17 to the memory 25 is stored in thememory and the addresses of the stages in which data is stored aredetermined by the input counters 32, 33, 34, and 35.

Each of the input counters 32, 33, 34, and 35 is a modulo-896 counter.Each state of a counter designates a stage of the memory 25 for thecorresponding quadrant. This address information passes from the inputcounters through the multiplexer 36 and the multiplexer 28 to the memory25. Thus, data is loaded in sequence into the 896 stages of eachquadrant of the memory.

' The rate at which data is entered into the memory is determined by therate at which each input counter changes state, or the rate of inputpulses to the counter. As explained previously, the input to-thecounters'is individually determined by the manually-operated ratecontrol switches 29 which set the output gates of the divider and gatesarrangement 31. A single oscillator 30, which in the specific embodimentoperates at a frequency of approximately 960 hertz is shown in FIG. 1.In order to avoid problems of timing interference, the oscillator 30 issynchronized by the master timer 61 to produce one pulse for every 32scan-lines. Pulses from the oscillator 30 are applied to the counters32, 33, 34, and 35 by the divider and gates 31 at sub-multiples of thisrate, specifically either approximately 240 hertz, hertz, or 60 hertz,as selected by the rate control switches 29. Individual oscillators andother pulse rates may be employed with some increase in the complexityof the circuitry in order to prevent timing interference.

Thus, the data presented to each waveform input channel may be loadedinto its corresponding quadrant of the memory 25 at an individuallyselected rate which determines the rate at which the image of thewaveform moves across the face of the display. This relationship willbecome more apparent from the discussion of the manner in which data isread out of the memory and presented to the display in a subsequentsection of this application.

As mentioned previously, alphanumeric information is applied at thealphanumeric input in digital coded format and includes the memoryaddress. The information is stored in the alphanumeric register'27. Thealphanumeric character data is then passed through the multiplexer 18and the address data through the multiplexer 28 to place the data in theproper stages of the memory 25.

FIG. 4 diagrams a cycle of writing information into the memory 25 andreading information out of the memory. Each cycle equals the period of asingle vertical scanline (32.5 microseconds). Information is writteninto the memory during a time period equal to the retrace time of 6.5microseconds. (Since there are propagation delays throughout the system,this portion of the cycle does not exactly coincide in real time withthe retrace period of the cathode ray tube beam.)

As illustrated in FIG. 4 this portion of the cycle is divided into fouroperations. During the first operation the alphanumeric data stored inthe alphanumeric register 27 is written into the memory by themultiplexers 18 and 28. During the second period the waveform data whichis about to be replaced with new data may be read out. (The particularstages containing this data are designated by the states of the inputcounters 32, 33, 34, and 35.) This particular operation takes place onlyif it is desired to otherwise store or record the data before it isdiscarded.

During the third period the waveform data stored in the register 17 iswritten into the proper stages of the appropriate quadrants of thememory by the multiplexers l8, and 36 and 28. These are the only periodsof the memory cycle which are utilized to write data in the memory 25.Since in the specific embodiment under discussion the memory 25 is andynamic MOS type, a memory refresh period is provided during which theexisting charges on the memory storage devices are restored, as is wellunderstood in the art, to prevent loss of data by leakage.

Data Output Waveform data is read out of the memory 25 for display undercontrol of the input counters 32, 33, 34, and 35 and the output counters71, 72, 73, and 74. The manner in which these elements address thememory to read data from the proper stages will be described in detailin a subsequent section of this application.

As indicated in the diagram of FIG. 4, for each scanline data pertainingto each waveform is read out of two stages of the memory 25. One pieceof data is designated the present data which may be considered ascorresponding to the specific scanline about to be traced. The other,designated the previous data, is stored in the stage of next lower orderthan the stage containing the present data, and concerns the sample ofthe waveform taken immediatelypreceding that related to the presentdata.

During the read waveform present period of the memory cycle (FIG. 4) thepresent data is read out of the appropriate stage of the memory 25 andstored in the waveform present register 42. During the read waveformprevious period the data in the stage immediately preceding the stagecontaining the present data is read out of the memory and stored in thewaveform previous register 41. The values of the data stored in theregisters 41 and 42 are compared by the comparator 44 and a count equalto the smaller value is entered in the small number counter 51 and acount equal to the larger value plus a small constant value is enteredin the large number counter 52. In the system as illustrated each pieceof data contains seven bits providing up to 128 possible values. In thisparticular case the smaller the value of the count the larger theamplitude or height of the sampled increment of the signal.

Clock pulses are applied to the small number and large number counters51 and 52 by the master timer 61. These pulses are synchronized with thetracing of each vertical scanline of the cathode ray tube beam whereby128 clock pulses correspond to 128 equallyspaced points along a scanlinewithin a quadrant. The 128 clock pulses may correspond to the tracingacross all five sectors of the first quadrant, for example.

The counters 51 and 52 count downward on the clock pulses. When thesmall number counter 51 reaches a count of zero, the flip-flop 54 isset. During the period the pulses are being counted, the scanline tracesdownward a distance which is equivalent to the time period measured bythe count. With the flip-flop 54 in its set condition it produces anoutput signal to the summation network 55 which enters the compositevideo signal as an unblanking signal causing an image to be written onthe surface of the cathode ray tube display 10. The beam thus beginswriting at this point on the face of the cathode ray tube to provide avisua image representing the value of the count.

The writing on the face of the display device continues tracing avertical line downward along the path of the scanline until the largenumber counter 52 counts downward to zero. When this event occurs, thelarge number counter 52 produces an output signal to the flip-flop 54resetting the flip-flop 54. Thus, the signal to the summation network 55is terminated and the unblanking signal is removed from the compositevideo signal whereby writing of the image ceases.

FIG. 5 depicts a small portion of the display surface of the displaydevice 10 illustrating the manner in which images of waveform data arewritten on the surface to construct a visual image of a waveform. InFIG. 5 the waveform, present data point corresponding to each scanlineis indicated by a mark at the right of the written image. (These marksdo not appear on the actual display, and are employed in FIG. 5 only forpurposes of explanation.) It can be seen that the image written duringeach scanline begins at the point representative of the larger of thepresent or previous data values.

In the display shown in FIG. 5 it is assumed for purposes ofillustration that there is no change in the data stored in the memoryduring the complete frame of both an odd and an even field. Thus, theprevious data value for each scanline is the present value for thescanline immediately to its left. As explained previously, the completeimage written during each vertical scanline extends from a pointrepresenting the larger value of the present or previous data to a pointrepresenting the smaller value. In addition, the written image isextended downward an additional fixed distance, by virtue of theadditional small constant value added to the large number counter 52 toprovide a minimum base line throughout the waveform.

Thus, as illustrated by FIG. 5, the displayed waveform is constructed ofa plurality of images which are lines between two datapoints rather thanof a plurality of separate dot images each at a single data point. Sinceeach data point of the waveform is connected to an adjacent data point,there are no gaps in the visual display when two adjacent values arewidely separated in amplitude. The apparatus thus produces displayswhich retain clarity, coherence, and usefulness at much steeperwaveformtransitions than heretofore possible. In addition, by broadeningthe base line in a controlled manner the aesthetic qualities andreadability of the display are further enhanced. 1 As indicated by thechart of FIG. 4 each of the fou rows of alphanumeric code words are readout of the memory during different periods of the memory cycle. Thealphanumeric code words are read out of the memory 25 under control ofthe alphanumeric refresh address counter 60 as will be explainedhereinbelow and are stored in the alphanumeric code register 43. Thecharacter code data in the register 43 is applied to the alphanumericcharacter generator 45. The alphanumeric character generator 45 is alsoconnected to the alphanumeric refresh address counter 60. Thealphanumeric character generator 45 may be any of the wellknown types ofread only memories which provide appropriate output signals in responseto the code information designating particular characters as supplied bythe register 43 together with data identifying each particular dotcolumn employed in constructing the character as supplied by thealphanumeric refresh address counter 60. in the specific embodimentbeing discussed, each alphanumeric character is constructed on thedisplay of five vertical columns of dots plus two columns of spacingbetween adjacent characters. Each dot column is traced by fourscanlines, two in each field, a total of 14 scanlines per field. Sincetwo scanlines of each field trace through the same dot column,information as to odd or even fields is not required by the alphanumericcharacter generator 45. The output signals from the alphanumericcharacter generator 45 are stored in a parallel-to-serial converterregister 53 and then shifted out to the summing network 55 to becomepart of the composite video signal to the display device Thus, for eachvertical scanline appropriate waveform and alphanumeric data is read outof the memory 25, converted to appropriate signals, and entered into thecomposite video signal. The operation repeats for each quadrant duringeach scanline. There are propagation delays and buffering delaysthroughout the system. However, the fixed relationship of timing signalsand delays in the variousportions of the system are such that unblankingsignals enter the composite video signal at the proper times so thatimages are written at the proper positions during each verticalscanline.

Data Output Control As mentioned previously, the addresses of the stagescontaining waveform data to be read out are controlled by the inputcounters 32, 33, 34, and 35 and the output counters 71, 72, 73, and 74.At the start of each field the contents of the input counters 32, 33,34, and 35 are entered in the output counters 71, 72, 73, and 74,respectively. Thus, the output counters contain data identifying thestages of the memory in which are stored the most recent sampled data onthe respective waveforms as of the beginning of the field. The pieces ofdata in these stages arethe present waveform data for the first scanlinein the odd field.

The output counters 71, 72, 73, and 74 are also modulo-896 countersarranged to count downward on clock pulses supplied by the master timer61. In the system being described the output counters are arranged tocount downward because successive pieces of data are placed in thememory at stages of successively higher order. Thus, in reading out datain reverse order (most recent data first, oldest data last) the stagesmust be addressed in downward order. The data is read out in reverseorder because the raster scanline pattern sweeps across the displaysurface from right to left and the most recent data appears at the rightof the display.

The manner in which the proper memory stages are addressed by the outputcounters for reading out data for each quadrant may best be explained byreference to the table of FIG. 6. For purposes of illustration it isassumed that the count of the-input counters 32, 33, 34, and 35 astransferred to the output counters 71, 72, 73, and 74, respectively, at.the start of an odd-field are 215, 701, 2, and 105, respectively. Forthe first useable scanline in the odd field the count of 215 in thefirst output counter 71 is applied through the multiplexers 57 and 28 toaddress the 215th stage of the memory which contains the present datafor the first quadrant of the first scanline. That data is read out ofthe 215th stage of the memory and entered in the waveform presentregister 42.

To obtain the address of the previous data, the first output counter 71counts down by one to a count of 214. Stage 214 is addressed through themultiplexers 57 and 28 causing the data stored therein to be read out tothe waveform previous register 41. The two pieces of data in theregister 41 and 42 are processed as explained previously to produceunblanking signals in the composite video signal.

a the multiplexers 57 and 28 as indicated in FI G[6. The

second output counter 72 then counts down by one to a count of 700, andthis address information is applied to the memory 25 throughthemultiplexers 57 and 28. As indicated in FIG. 6, the foregoing proceduresare repeated for addressing the memory to obtain the present'andprevious data forthe first scanline of the waveform of the third andfourth quadrants.

Upon completion of the first scanline of the odd field, the first outputcounter 71 counts downward by one to start the second scanline in theodd field with a count of 213. The displacement of the count by two fromthe count of 215 at the start of the first scanline is necessary becausethe scanlines are interlaced for the odd and even fields. Thus, the213th stage of the memory is addressed to read out the present data forthe first quadrant of the second scanline, and the 212th stage isaddressed for the previous data. The procedure continues in order toaddress the memory for reading out the present and previous data for theother waveforms as controlled by the decreasing counts in theotheroutput counters. 3

For the start of the third scanline in the odd field the starting countin the first output counter 71 is 21 l. The action continues until theodd field has been traced producing images of the waveforms on thedisplay surface. Since the memory is continually being updated with morerecent data during the time the odd field is being swept, the data inthe last few stages which contained the oldest data at the start of thefield are not displayed. In the specific embodiment as disclosed, thelast eight stages in each address sequence for a field are not displayedin order to insure that no recently sampled increments of the waveformswill appear out of position.

After completion of the tracing of the odd field and at the start of theeven field, the counts in the output counters 71, 72, 73, and 74 arereplaced by the updated counts in the input counters 32, 33, 34, and 35,respectively. The addressing procedure is carried out in a similarmanner for the even field in which the scanlines are traced between thescanlines of the odd field. Since under usual operating conditions newdata was entered into the memory during the tracing of the odd field,the first stage addressed is of higher order. Thus, the data isdisplayed during the even field to the left of its position during theprevious odd field producing an appearance of movement of the waveformsfrom right to left.

In contrast, the alphanumeric characters remain fixed in the sameposition on the display surface of the display device during subsequentsweeps of the raster scanline pattern. As explained previously, the6-bit code words employed to designate any of 64 possible alphanumericcharacters are read out of the memory and stored in the alphanumericcode register 43 for transfer to the alphanumeric character generator45.

The addresses of stages to be read out are controlled by thealphanumeric refresh address counter 60 in a cyclical operation which isrepeated for each field. The alphanumeric refresh address counter 60addresses the proper stages of the memory and also provides informationto the alphanumeric character generator 45 identifying the dot column ofthe character.

A more detailed block diagram of the alphanumeric refresh addresscounter 60 is shown in FIG. 7. The alphanumeric refresh address counter60 includes a modulo-16 counter 62 the output of which is applied to amodulo-l4 counter 63, the output of which in turn is applied to amodulo-32 counter 64. The master timer 61 supplies l6 periodic clockpulses to the modulo-l6 counters 62 for each scanline. The count in themodu- 10-16 counter 62 is detected and applied to the memory 25 by wayof multiplexer 28 to select the quadrant and also the row within thequadrant. The address information also includes a constant to restrictthe address to stages 896 through 1,023 of the memory 25.

The modulo-14 counter 63 receives one input pulse from the modulo-l6counter 62 for each vertical scanline. The count in the modulo-l4counter 63 is detected and applied to the alphanumeric charactergenerator 45 to identify the dot column being traced as a particular oneof the seven dot columns of a character (Each dot column includes twoscanlines of each field.) The modulo-l4 counters 63 provides a pulse tothe modulo-32 counter 64 for each 14 scanlines (corresponding to theportion of a character displayed during one field). The detected countof the modulo-32 counter 63 combined with the row address informationfrom the modulo-l6 counter 62 provides the address to a particular stageof a quadrant of the memory. The memory address information passes fromthe alphanurneric refresh address counter to the memory 25 through themultiplexer 28.

The operating cycle of the alphanumeric waveform refresh address counter60 is identical for each field. Thus, the proper signals for writing thecharacter are loaded into the parallel-to-serial register 53 and leavethe register 53 at the proper time to combine with other signals in thesummation network 55 to become part of the composite video signal asexplained previously. Since the stages of the memory 25 are addressed atthe same time during each sweep of the raster scanline pattern, thealphanumeric characters appear fixed in the same position on the face ofthe display despite the movement of the waveforms.

Conclusion In summary, the system as shown and described receivestime-varying analog waveform signals on any of up to four separate inputchannels and stores digital representations of samples of the signals inthe random access storage memory 25. The time span of the portion of awaveform encompassed by the total number of stored representations maybe varied individually by varying the input rate of pulses to therespective input counters 32, 33, 34, and 35 thereby controlling therate at which waveform data is entered into the memory 25.

The stored waveform data for each channel is read out in sequence foreach sweep of the raster scanline pattern and displayed visually on thedisplay device 10 to produce a waveform with the most recent data at theright. As the data in the memory is continually updated, the waveformdata appears to be moving from the right to the left of the displaysimulating a view of a stripchart recorder through a window. Since therate at which the data in the memory is updated is controlled bycontrolling the rate at which pulses are applied to the input counters32, 33, 34, and 35, the time span encompassed by the data displayed andthe rate at which a waveform moves across the display are alsocontrolled thereby. The rate of entry of data into the memory can becontrolled individually for each of the four channels. The rate of entrycan be reduced to zero whereby the data stored in the memory does notchange and the same portion of a waveform is displayed continuously onthe surface of the display device with its movement frozen.

By virtue of the arrangements employed to store the waveform data andcontrol the writing in and reading out of the data from the memory,additional information may be displayed in fixed positions on thedisplay surface. As described herein up to four rows of 32 alphanumericcharacters may be displayed in each quadrant in association with awaveform. Alphanumeric data is displayed in predetermined positions onthe display surface by virtue of its address when written into thememory. I

In addition, the apparatus as shown includes a timing mark generator 20.When activated this generator operates on a timed multiple of the rasterscanline time to insert an unblanking signal intothe composite videosignal at the summing network 55. For example, every 24th scanline ofeach field may be unblanked to produc a pattern of equally-spacedvertical double-lines on the display surface. An observer can countthese timing marks to obtain a measure of the correspondence of awaveform image to real time.

An erase code generator 19 when activated inserts a constant digitalvalue into all the stages of the memory containing waveform data duringthe write waveform portion of a memory cycle (FIG. 4). Thus, all thestored waveform data is removed from the memory during a single retraceperiod so that the entire display is erased in a single frame.

During the read waveform portion of the memory cycle (FIG. 4) data maybe read out of the stage of the memory containing the oldest stored dataprior to its being replaced by the incoming most recent data. Asexplained previously, this data may be recorded for retention. Inaddition, the data in one quadrant may be read out, placed in atemporary register 26, and then reinserted through the multiplexer 18 inanother quadrant of the memory. In this way two, three, or four displayquadrants may be employed to display two, three, or four continuousportions of a single waveform, cascading the images from one quadrant tothe next.

While there has been shown and described what is considered a preferredembodiment of the present invention, it will be obvious to those skilledin the art that various changes and modifications may be made thereinwithout departing from the invention as defined in the appended claims.

What is claimed is:

1. Apparatus fordispl aying time-varying signals including incombination means for receiving a time-varying signal;

sampling means for periodically sampling said signal;

means for converting the samples of the signal to digitalrepresentations thereof;

memory means for storing a predetermined number of said digitalrepresentations; input control means for loading the most recent digitalrepresentation into the memory means in place of the oldest digitalrepresentation stored therein;

display means of the type producing images on a display surface byselectively writing on the display surface while repeatedly sweeping araster scanline pattern over the display surface;

output means coupled to the memory means and the display means forcausing two digital representations read out of the memory means foreach scanline of the raster scanline pattern to produce an image on thedisplay surface during tracing of the scanline from a pointrepresentative of the value of 1 one digital representation to a pointrepresentative of the value of the other digital represenation; andoutput control means for reading out two digital representations fromthe memory means for each scanline of the raster scanline pattern andfor causing digital representations to be read out in synchronism withthe sweeping of the raster scanline pattern to cause images of the mostrecent digital representations to appear at one edge of the display andimages of the oldest digital representations to appear at the oppositeedge of the display.

2. Apparatus for. displaying time-varying signals in accordance withclaim 1 wherein said display means traces each individual scanline ofsaid pattern in a direction substantially orthogonal to the line ofdirection from said one edge of the display to said opposite edge of thedisplay, 3. Apparatus for displaying time-varying signals in accordancewith claim 2 wherein said output means includes first counting means formeasuring a first time period representative of the value of one of thedigital representations read out of the memory means for each scanlineand for producing a first output signal at the termination of the firstmeasuredtime period, second counting means for measuring a second timeperiod'representative of the value of the other of the digitalrepresentations read out of the memory means for each scanline and forproducing a second output signal at the termination of the secondmeasured time period, and flip-flop means coupled to the first andsecond counting means and operable to produce an un- 5 blanking signalin response to a first output signal and toterminate the unblankingsignal in response to a second-output signal; said display means beingoperable to produce images by writing on the display surface during anunblanking signal; and including means for synchronizing the start ofmeasuring each of said time period with the tracing of each scanline tocause an unblanking signal to produce images along the scanline betweenpoints corresponding to the values of the two digital representations.4. Apparatus for displaying time-varying signals in accordance withclaim 3 wherein said first counting means includes first means forreceiving a count representative of the value of one of the digitalrepresentations read out of the memory means for each scanline, andsecond means for receiving periodic clock, pulses and for producing saidfirst output signal when the number of clock pulses received equals thecount received from said first means; said second counting meansincludes first means for receiving a count representative of the valueof the other of the digital representations read out of the memory meansfor each scanline, and second means for receiving periodic clock pulsesand for producing said second output signal when the number of clockpulses received equals i the count received from said first means of thesecond counting means; and including means for applying periodicclockpulses to the second means of the first and second counting meanswhen activated; and further wherein said means for synchronizing isoperable to activate said means for applying periodic clock pulses atthe same point during each trace of a scanline. 5. Apparatus fordisplaying time-varying signals in accordance with claim 4 wherein saidoutput means includes first register means coupled to said memory meansfor receiving and storing one of the digital representations read out ofthe memory means for each tracing of a scanline, second register meanscoupled to said memory means for receiving and storing'the other of thedigital representations read out of the memory means for each tracing ofa scanline, and

comparison means coupled to the first and second register means and tosaid first means of the first counting means and said first means of thesecond counting means, said comparison means being operable to comparethe digital representations stored in the first and second registermeans and to transmit counts representative of the value of each of thetwo digital representations to said first means, the smaller count beingtransmitted to the first means of the first counting means and thelarger count being transmitted to the first means of the second countingmeans. 6. Apparatus for displaying time-varying signals in accordancewith claim wherein said memory means includes a random access memorymeans having a plurality of stages, each of which is capable of storinga digital representation;

said input control means is operable to load digital representations insequence into said stages, each digital representation being loaded intoa stage in place of the oldest digital representation stored in thememory means;

said output control means is operable to cause digital representationsto be read out of two adjacent stages for each scanline by addressingpairs of adjacent stages in succession, the first stages to be addressedin each succession being changed during subsequent successions inaccordance with the replacement of old digital representations by newdigital representations, while the digital representations remain in thesame stages except to be re moved from the memory means and replaced bymore recent digital representations, in order that images of the mostrecent digital representations appear at said one edge of the displayand images of the oldest digital representations appear at said oppositeedge of the display.

7. Apparatus for displaying time-varying signals in accordance withclaim 6 wherein said input control means includes input counting meansfor counting input clock pulses through a recurring sequence of statesequal in number to the number of the plurality of stages in the randomaccess memory means,

input pulse means coupled to the input counting means for applyingperiodic input clock pulses thereto,

said input counting means being coupled to the random access memorymeans and being operable to control the address of the stage in which adigital representation from said means for converting is loaded inaccordance with the state of the input counting means whereby each inputclock pulse causes a digital representation to be loaded into the nextstage in a repeating succession corresponding to the recurring sequenceof states of the input counting means; and i said output control meansincludes means coupled to the input counting means for determining thestate of said input counting means, and

output address means coupled to the random access memory means and tosaid last-mentioned means and operable to address pairs of adjacentstages in sequence in accordance with the state of the input countingmeans in synchronism with the sweeping of the raster scanline pattern tocause pairs of digital representations to be read out of the memorymeans in sequence and images thereof to appear on the display withimages of the most recent digital representations at said one edge ofthe display and images of the oldest digital representations to appearat said opposite edge of the display.

1. Apparatus for displaying time-varying signals including incombination means for receiving a time-varying signal; sampling meansfor periodically sampling said signal; means for converting the samplesof the signal to digital representations thereof; memory means forstoring a predetermined number of said digital representations; inputcOntrol means for loading the most recent digital representation intothe memory means in place of the oldest digital representation storedtherein; display means of the type producing images on a display surfaceby selectively writing on the display surface while repeatedly sweepinga raster scanline pattern over the display surface; output means coupledto the memory means and the display means for causing two digitalrepresentations read out of the memory means for each scanline of theraster scanline pattern to produce an image on the display surfaceduring tracing of the scanline from a point representative of the valueof one digital representation to a point representative of the value ofthe other digital represenation; and output control means for readingout two digital representations from the memory means for each scanlineof the raster scanline pattern and for causing digital representationsto be read out in synchronism with the sweeping of the raster scanlinepattern to cause images of the most recent digital representations toappear at one edge of the display and images of the oldest digitalrepresentations to appear at the opposite edge of the display. 2.Apparatus for displaying time-varying signals in accordance with claim 1wherein said display means traces each individual scanline of saidpattern in a direction substantially orthogonal to the line of directionfrom said one edge of the display to said opposite edge of the display.3. Apparatus for displaying time-varying signals in accordance withclaim 2 wherein said output means includes first counting means formeasuring a first time period representative of the value of one of thedigital representations read out of the memory means for each scanlineand for producing a first output signal at the termination of the firstmeasured time period, second counting means for measuring a second timeperiod representative of the value of the other of the digitalrepresentations read out of the memory means for each scanline and forproducing a second output signal at the termination of the secondmeasured time period, and flip-flop means coupled to the first andsecond counting means and operable to produce an unblanking signal inresponse to a first output signal and to terminate the unblanking signalin response to a second output signal; said display means being operableto produce images by writing on the display surface during an unblankingsignal; and including means for synchronizing the start of measuringeach of said time period with the tracing of each scanline to cause anunblanking signal to produce images along the scanline between pointscorresponding to the values of the two digital representations. 4.Apparatus for displaying time-varying signals in accordance with claim 3wherein said first counting means includes first means for receiving acount representative of the value of one of the digital representationsread out of the memory means for each scanline, and second means forreceiving periodic clock pulses and for producing said first outputsignal when the number of clock pulses received equals the countreceived from said first means; said second counting means includesfirst means for receiving a count representative of the value of theother of the digital representations read out of the memory means foreach scanline, and second means for receiving periodic clock pulses andfor producing said second output signal when the number of clock pulsesreceived equals the count received from said first means of the secondcounting means; and including means for applying periodic clock pulsesto the second means of the first and second counting means whenactivated; and further wherein said means for synchronizing is operableto activate said means for applying periodic clock pulses at the samepoint during each trace of a scanline.
 5. Apparatus for displaYingtime-varying signals in accordance with claim 4 wherein said outputmeans includes first register means coupled to said memory means forreceiving and storing one of the digital representations read out of thememory means for each tracing of a scanline, second register meanscoupled to said memory means for receiving and storing the other of thedigital representations read out of the memory means for each tracing ofa scanline, and comparison means coupled to the first and secondregister means and to said first means of the first counting means andsaid first means of the second counting means, said comparison meansbeing operable to compare the digital representations stored in thefirst and second register means and to transmit counts representative ofthe value of each of the two digital representations to said firstmeans, the smaller count being transmitted to the first means of thefirst counting means and the larger count being transmitted to the firstmeans of the second counting means.
 6. Apparatus for displayingtime-varying signals in accordance with claim 5 wherein said memorymeans includes a random access memory means having a plurality ofstages, each of which is capable of storing a digital representation;said input control means is operable to load digital representations insequence into said stages, each digital representation being loaded intoa stage in place of the oldest digital representation stored in thememory means; said output control means is operable to cause digitalrepresentations to be read out of two adjacent stages for each scanlineby addressing pairs of adjacent stages in succession, the first stagesto be addressed in each succession being changed during subsequentsuccessions in accordance with the replacement of old digitalrepresentations by new digital representations, while the digitalrepresentations remain in the same stages except to be removed from thememory means and replaced by more recent digital representations, inorder that images of the most recent digital representations appear atsaid one edge of the display and images of the oldest digitalrepresentations appear at said opposite edge of the display. 7.Apparatus for displaying time-varying signals in accordance with claim 6wherein said input control means includes input counting means forcounting input clock pulses through a recurring sequence of states equalin number to the number of the plurality of stages in the random accessmemory means, input pulse means coupled to the input counting means forapplying periodic input clock pulses thereto, said input counting meansbeing coupled to the random access memory means and being operable tocontrol the address of the stage in which a digital representation fromsaid means for converting is loaded in accordance with the state of theinput counting means whereby each input clock pulse causes a digitalrepresentation to be loaded into the next stage in a repeatingsuccession corresponding to the recurring sequence of states of theinput counting means; and said output control means includes meanscoupled to the input counting means for determining the state of saidinput counting means, and output address means coupled to the randomaccess memory means and to said last-mentioned means and operable toaddress pairs of adjacent stages in sequence in accordance with thestate of the input counting means in synchronism with the sweeping ofthe raster scanline pattern to cause pairs of digital representations tobe read out of the memory means in sequence and images thereof to appearon the display with images of the most recent digital representations atsaid one edge of the display and images of the oldest digitalrepresentations to appear at said opposite edge of the display.